Mineral wool, in particular stone wool and glass wool, is used in numerous applications in various forms, for instance for sound insulation, heat insulation, fire protection, construction applications and as a horticultural growth substrate.
Once the product is no longer required, there is a need to dispose of it in an appropriate manner. This is potentially problematic in the case of mineral wool which has been used in a variety of applications, and in particular in the case of mineral wool which has been used as a horticultural growth substrate. This material eventually comes to the end of its useful life and must be disposed of. It is desired to reuse the product in some way rather than, say, sending it to landfill. However, this is not straightforward, because the end-of-life product has within it high levels of water including nutrients and other components used by the growers such as trace elements (often above 10% by weight of the substrate) and contains organic plant material and is usually surrounded by other, often organic, material, such as polymeric film.
At present, a common method of disposing of this material is by using it for the fabrication of bricks, after separating the polymeric packaging from the mineral wool growth substrate and pre-treating the waste growth substrate.
Other methods of treating waste stone wool material are known. Such methods often involve grinding the waste material in the presence of a liquid such as water. Often a binder (organic or inorganic) is added to the ground base material. The mixture can be shaped to various forms and the shaped bodies are then dried.
For instance, JP 10279936 discloses a method for recycling building waste including concrete, rock wool, timber chips, etc. This method comprises (a) recovering the waste, (b) sorting the waste, (c) pulverizing and mixing the waste, (d) adjusting the pulverized material to a desired size, (e) adding binder, which is cement milk in the case of concrete or rock wool, and mixing the blend, (f) press moulding the moulding material formed from the blend.
According to CN1128243, waste rock wool is produced through extrusion and shearing into grains, which are first mixed with cement, gypsum powder or other adhesive (binder) material and then adsorbed in certain amount of water to form a layer of enclosing film on the surface. Rock wool grains thus produced may be used as building material. No heating is mentioned.
In FR2781701A, there is disclosure of heat treatment of fibrous composites, of diverse origin, with a silica and magnesia base equally incorporating organic materials, which consists of: (a) mixing the composite in an intimate and homogeneous manner; (b) heating the mixture to 700 to 900 deg C.; and (c) simultaneously and separately recovering the combustion gas and the final inert composite. The composite may be asbestos, rock wool, glass wool or mixtures of these materials. The product of this method in the form of a ceramic composite is also claimed together with an installation for putting the method into service. The way of making the product does not mention a step of granulating.
JP9023743A describes a method in which ground waste rock wool is mixed with water and a binder such as one or more of guar gum, CMC and starch, and the mixture is subjected to the reduction of the water content to give a water content of 20 to 50%. The water-reduced mixture is extruded and ground. The produced particulate ground product is calcined at 1100 to 1190° C. to obtain a foam product having an apparent specific gravity of 0.3 to 0.5 g/cm3 and capable of being used as an artificial culture medium.
JP2002187751 describes a process in which powdered waste rock wool is granulated using an inorganic hydraulic binder and water. The granules are then dried. The content of rock wool is in the range 85 to 98%.
Other publications discuss recycling of glass wool.
For instance, JP2002348181A provides a glass wool sintered material having high utility value capable of effectively reducing the volume of glass wool and recycling waste materials, a method for manufacturing the glass wool sintered material, and some kinds of treated materials containing the glass wool sintered material. The glass wool sintered material is prepared by sintering a glass wool such as a waste glass wool. It is desirable that the specific gravity of the sintered material is 0.05 g/cm3 or more. The sintered material is manufactured by heat treatment of a glass wool at temperature of 600 to 900° C. It is desirable that the heating time is 1 to 90 minutes and the volume of glass wool after sintering is 0.4 or less against the volume 1 before sintering. The sintered material is used for tiles, ecosystem protective materials, soil materials, and aggregates.
US2005242477 provides a method to transform large quantities of fibre glass waste into useful ceramic products by a low-cost manufacturing process. The method consists of reducing the fibre glass waste into a glass powder; mixing the glass powder with additives into a glass-additives mixture; granulating the glass-additives mixture into granulated particles; forming the granulated particles into a green ceramic article; and heating the green ceramic article into the ceramic product. Water and clay can be included in the processing. Only one firing step is needed with a low peak firing temperature of about 700° C. to about 1000° C. The method is said to conserve energy and natural resources compared to clay-based traditional ceramic manufacturing. High-quality impervious ceramic products can be produced by the invention.
However, it is desirable to find alternative methods of recycling mineral wool substrates, in particular stone wool substrates, especially methods which are suitable for use with water-containing substrates such as those which have already been used for horticulture.
There is also a constant desire for new mineral-based products for use in the horticultural industry and in the construction and other industries. It would therefore be desirable to be able to provide a method which not only allows recycling of waste stone wool substrates but which results in a product which has a variety of uses in several fields, segments and markets.
In our co-pending application PCT/EP2008/068208, we describe one solution to this problem whereby we disclose a method of producing a granular product, the method comprising providing a base material in particulate form such that at least 80% by weight of the base material is in the form of particles having size not more than 20 mm, and comprises mineral wool, and has water content not more than 50 wt % based on the particulate base material, mixing the particulate base material with a binder material to form a base-binder mixture, forming the base-binder mixture into granules, wherein at least 80% by weight of the granules have size not more than 40 mm, and drying the granules, wherein at least 80% by weight of the product is in the form of granules having size not more than 40 mm. Drying the granules is by heating at a temperature in the range of from 700 to 1100° C.
Specifically, the waste mineral wool product includes waste horticultural growth substrate (usually including plant residues and polymeric film) and the base material is produced by providing mineral wool in coherent form having minimum dimension at least 50 mm and having a content of at least 10% water, by weight of the waste product; producing base material from the waste mineral wool product by reducing the coherent mineral wool to particulate form such that at least 80% by weight of the base material is in the form of particles having size not more than 20 mm, and has water content not more than 50 wt % based on the particulate base material.
We find that this method provides a number of benefits.
Firstly, it is a convenient way to recycle waste mineral wool substrate and is applicable even to difficult substrates such as those which have been used in horticulture and hence are wet and combined with organic material such as plant residues and their decomposition products and polymeric film packaging materials. Such substrates can be difficult to re-use, even in known ways such as by grinding and subsequent inclusion in briquettes for formation of a mineral melt, since the organic content tends to negatively affect the performance of the cement binder commonly used for such briquettes.
Furthermore, it results in a product having beneficial product properties and hence is useful even when the starting material is not a waste product (although use of a waste product has economic and environmental advantages).
However, we find that the obligatory inclusion of binder adds expense and additional technical constraints to the method and requires use of further resources (namely binder). This is undesirable especially in the context of a method which is intended to provide a means for re-using a waste product and hence to have environmental advantages.